fix: distinguish accounts by email and plan

[ThWink]

Summary

• distinguish saved ChatGPT accounts by record_key first, then normalized email + plan type
• allow the same email to keep separate Plus and Team archives instead of overwriting by email alone
• include regression tests for same-email/different-plan and same-email/same-plan identity matching

Root Cause

The archive lookup fell back to matching only the email address when record_key was not available. That caused accounts using the same email but different plans, such as Plus and Team, to be treated as the same saved account.

Validation

• python -m unittest discover -s . -p 'test_*.py'
• python codex-switcher.py --help